Method of manufacturing boxes of cardboard



y 1961 F. K. KNUTSSON-HALL 2,985,075

METHOD OF MANUFACTURING BOXES OF CARDBOARD Filed Jan. 29, 1957 FIG.1

tes Patent 05cc 2,985,075 Patented May 23, 196i METHOD OF MANUFACTURING BOXES F CARDBOARD Folke Knnt Knntsson-Hall, 34 Strandvagen, Falkenberg, Sweden Filed Jan. 29, 1957, Ser. No. 637,026

Claims priority, application Sweden Feb. 20, 1956 8 Claims. (Cl. 93-36) The present invention relates to a method of producing boxes of cardboard.

Hitherto such boxes have substantially been made in such a manner that that portion which is to form the edges of the box has been marked, whereafter the cardboard has been folded so that sides are made. This method suifers from the disadvantage that the angles, after the sides have been formed, are not fixed, but change easily due to pressure and the like, whereby the form of the box will be changed.

Further the dimensions of the cardboard itself will be somewhat changed at the folding operation, as a minor stretching laterally of the cardboard occurs along the indicating lines. Furthermore there will be an elevation of the cardboard along the lines of indication which impairs the cardboard when the boxes shall be pressed or fed forwards by precision folding machines.

In order to avoid these disadvantages outwardly diverging grooves may be made in the cardboard, for example by means of grinding Wheels and the like along the edges bounding the sides of the box to be formed.

In the accompanying drawing a cardboard blank is shown in which such grooves have been made.

Fig. 1 shows a piece of cardboard or a blank for a box, provided with indicating cuts. Fig. 2 shows the blank after having been folded into the form of a box. Fig. 3 shows a cut, the folding being intended for 90, and Fig. 4 shows the same cut after the cardboard blank has been folded 90.

Referring now to the drawing reference 2 designates marking cuts, 3 designates the surface of a box,-4 designates the sides of the cuts and 5 designates a folded cut.

It has appeared, however, that the operation of glueing the blanks together so that finished boxes are formed is connected with certain difliculties, when a rapid binding is to be attained, for example in rapidly running machines for the production of the boxes. Usual binding agents in solution and paste and the like bind too slowly and methods of the kind called for example the quick binding method suffer from great disadvantages. This method consists therein that the surface of one of the flaps of the cardboard blank, which are to be glued together, is coated with glue at an early stage and is allowed to dry before the blanks are folded-in the machines. Due to the fact that the surface of the second flap is coated with glue solution or is moistened, this flap adheres comparatively quickly to the layer of dried glue of the other flap. The disadvantages of this method are first of all that an extra glueing operation is required, before the blanks are brought to the machines. Secondly, the dried film of glue on the flap obstructs the feed of the blanks in rapidly running machines and a small quantity of moisture may cause boxes piled upon each other to be glued together.

Furthermore it has appeared that the rapidly working elements of the box machines will easily be besmeared with glue and the like, which obstructs the perfect work of the machine.

Usual paste or glue solution must be of so high a concentration in order to be able to bind quickly, even when heat is supplied, that the paste, the glue solution or the like obtains such a hardness, that it is not possible to use quickly acting binding agents owing to the said high concentration.

It has appeared that another method must be employed. This method consists therein that instead of paste or another binding agent the binding substance in itself is used, suspended for example in cold water or in some other suitable liquid. Then a very fluent slurry is obtained containing the binding substance. This slurry has no binding ability, but it contains such an amount of the binding substance, that, in pasted condition, it is too hard and too viscous to be used. This slurry does not damage the elements or loose parts of the machine and does not make them sticky. If, for example, through a suitable arrangement, one of the flaps 3 to be glued, is coated with such slurry, the said flap will become wet. Some of the liquid penetrates into the cardboard material, whereby the latter will become more flexible. Thereby the binding substance in the slurry will be more abundant on the surface of the cardboard. If then the other of the two flaps which are to be glued, is put together with'the first one, and the joint is heated by being allowed to pass for example a templet, which is heated, then a thin layer of very abundant paste or the like is formed, owing to the increase of temperature, between the flaps, and binding takes place almost instantaneously. Starch, for example potato flour, suspended in water, may be used with great advantage. The film of starch formed will be greatly adhesive and comparatively moisture-resistant.

As another example may be mentioned polyvinyl acetate powder, not emulsified but suspended in cold water. In such a case a very strongly adhesive layer, which is moisture-resistant, is obtained between the flaps. Also other thermoplastic substances can be used in the same way, such as cellulose butyrate, natural resins, synthetic resins, plastic materials and the like. The flaps are joined as soon as the temperature, when they pass the said heated templet, has increased sufficiently for the binding agent, and as regards potato flour and polyvinyl acetate for example and up to is a suitable temperature in the layer between the flaps of cardboard, when these pass the heated templet. The heating may be effected for example by an electrical resistor or the like and can be controlled in the usual manner by means of a thermostat.

Generally water can be used as liquid for the slurry of the pulverized binding substance, and besides water alcohol or some kinds of mineral oil can be used for certain binding agents, for example butyrates, or for certain powders of plastic.

In this way glueing or pasting together, suitable for the speed of the machine, can be brought about in rapidly working machines, without it being necessary to resort to dryu'ng and without impairing the capacity and the function of the machine, and this method of glueing is advantageous to all blanks, either the edges of the box are traced or marked in some other way.

As mentioned above, the heat, with regard to different binding agents, can be regulated by means of a thermostat in such a manner that the temperature suitable for the binding agent is obtained. The amount of binding substance in the slurry can be varied, and if porous cardboard is used, the amount of binding substance in the slurry can be reduced, as the cardboard absorbs some of the liquid in which the binding substance has been suspended, and thereby the amount of binding substance in the slurry is increased in that layer that remains on the surface of the cardboard. Variations for different kinds of cardboard are easily brought about, so that, for example for certain porous types of cardboard an amount of 20% of binding substance in the slurry can be used. Usually an amount of 30-40% of binding substance is suificient, depending upon what has been stated above.

Under certain circumstances, for example when plain cardboard surfaces shall be joined, the liquid in which the slurry is suspended, is made more or less viscous in order to prevent the binding agent in the slurry, for example when a stirrer cannot be used, from separating from the liquid and depositing at the bottom. A thin paste may be used, for example starch, cellulose ethylate or the like, and in this thin paste the pulverized binding substance is suspended, which, owing to the comparatively viscous suspension liquid, then is relatively evenly distributed in the liquid.

If traced grooves which are diverging outwardly are used in the production of boxes, the result, when the sides are folded inwardly, will be that the surfaces 4 of the grooves will coincide approximately (see 5 in Fig. 4).

As the cuts cannot be made as deep as the thickness of the cardboard, a certain resistance to bending will arise when the cardboard is folded, which to a rather great extent prevents rapidly working machines from working perfectly.

If the traced grooves are coated with a binding agent, the sides of the grooves at the folding will be glued together, which results therein that the edges of the box will receive increased strength, and the weakening due to the fact that material, when the groove was made, was removed from the cardboard, can be compensated for.

If sticky or pasty binding agents are used, it will be diflicult to provide the insides of the grooves 4 with such a binding agent, as the more viscous binding agent Will not flow down into the grooves but remain at the upper edges, and therefore the result of the glueing will not be satisfactory.

Boxes produced in this way will often be besmeared at the inner side, and a binding agent which may have been disposed outside the grooves along the upper edges thereof, may prevent a rapid production, as the box or the blank may stick to folding elements or the like of the machine.

If binding substance slurry according to the invention is used, the conditions will be changed, as the relatively fluent slurry will be easily disposed in the grooves. Simple devices can be used, such as rotating wheels and thin brushes or the like, the outer periphery of which transfers slurry from a container to the grooves. Then the slurry spreads in the grooves, which involves a further advantage, as some of the liquid of the suspension, contrary to a viscous binding agent, pentrates quickly into the material and softens the cardboard of the grooves. The resistance to bending is reduced considerably on account thereof, so that the blanks are easily folded.

Furthermore the amount of binding agent in the slurry will increase owing to the fact that the cardboard absorbs some of the liquid. This is a very important fact, and after having been folded and after having been allowed to pass a heated templet, as described above, the grooves will receive a very great strength, which in the edges greatly exceeds that of the cardboard material. Boxes manufactured in this way will obtain a firm and strong shape.

If the blank shall be folded in two directions, for example in order to form bottom and lid, and the tracing therefore has been made in two directions, for example at angles to each other, this method may be used with advantage, and flaps and sides can be glued together, whereby boxes are formed which have great strength.

When boxes of cardboard are concerned, these may advantageously be made in such a manner that the cardboard is provided with the decorations and the print with which the finished boxes are to be provided.

When the blank is folded, the displacement of the material arising in the cardboard, impairs the cardboard of the edges. This is due to the fact that the grooves cannot be as deep as required for an imagined bending, for example at right angles.

However, it has appeared that, if cardboard is bent, for example along outwardly diverging traces, and if the grooves are provided with the abovementioned suspension, then the material of the groove will be displaced comparatively equally, so that the edges of the box formed will be relatively rectangular and even, without cracks arising in the cardboard or the decoration.

When the cardboard is to be bent less or more than 90, the same method may be used due to the fact that the Width of the widest part of the outwardly diverging marked line is made wider or narrower in proportion to the extent of the bending.

If marked lines as per above are provided with bind-' ing substance slurry, it has appeared, as mentioned above, that the displacement of material of the cardboard is considerably facilitated due to the fact that the liquid of the suspension softens the material, so that the sides of the grooves formed coincide well, and as the latter, by absorbing liquid, have been mixed with an abundant amount of the said suspension, the finished boxes, after having passed a heated templet or the like, will receive great strength, at the same time as the boxes will be formed perfectly in rapidly working folding machines.

What I claim is:

1. A method of manufacturing cardboard boxes having V-shaped grooves formed in the blanks at the fold lines thereof comprising first, the applying of a slurry containing a liquid vehicle and a binding substance to the faces of said groove; next, bending said blank until the faces of said groove are in abutting relationship; and, finally, applying heat and pressure to the thus folded grooved portion of the blank.

2. The method of claim 1 in which the binding substance is a thermoplastic material.

3. The method of claim 1 in which the binding substance is polyvinyl acetate powder.

4. The method of claim 1 in which the binding substance is a starch suspended in an aqueous vehicle, and in which the cardboard is heated to a temperature of from 90 to after application of the liquid suspension.

References Cited in the file of this patent UNITED STATES PATENTS 313,814 Davis Mar. 10, 1885 1,897,198 Keller Feb. 14, 1933 2,000,634 Du Brul May 7, 1935 2,633,063

Ohrn Mar. 31, 1953 

